The present invention generally relates to a solvent system for cellulose. More particularly, the present invention provides an amine-based solvent for cellulose, a cellulose composition comprising the same (e.g. a cellulose solution), and methods of making and employing the solvent and cellulose composition (e.g. a cellulose solution).
The dissolution of cellulose without chemical modification and/or derivatization is an extremely difficult task because it is a stiff molecule and it is characterized by close chain packing via numerous inter- and intramolecular hydrogen bonds. Since the 1970s novel solvents for cellulose based on the concept of xe2x80x9cno heavy metalsxe2x80x9d have been sought to replace the multistep, polluting viscose process. Several relevant reviews that address current efforts to provide celluose solvents are as follows: Hudson, S. M. and Cuculo, J. A., J Macromol Sci-Rev Macromol Chem (1980) C18 (1):1-82; Philip, B., J Macromol Sci-Pure and Apply Chem (1993) A30:703-714; Guo, J.-X. and Gray, D. G., in Cellulosic Polymers, Blends and Composites; Gilbert, R. D., Ed.; Hanser: Munich, Vienna, New York (1994), Chapter 2, pp 25-45; Cuculo, J. A., et al., in Polymeric Materials Encyclopedia, Salamone, J. C., Ed., CRC Press: New York (1996) Vol. 2, pp 1029-1035; Myasoedova, V. V., in Physical Chemistry of Non-aqueous Solutions of Cellulose and its Derivatives, Myasoedova, V. V., Ed.; Wiley: Chichester, (2000), Chapter 1, pp 3-36.
Currently, only the N-methylmorpholine-N-oxide (NMMO)/H2O system developed by Chanzy et al. (Chanzy, H., et al., J Polym Sci: Polym Lett Ed (1979) 17:219-226) has been industrialized for the solvent spinning of cellulose. The product spun by this process is sold under the registered trademarks TENCEL(copyright) and COURTAULDS LYOCELL(copyright) by Courtaulds Fibres (Holdings) Limited, London, England, United Kingdom. The advantage of this solvent is its ability to attain exceedingly high concentrations of cellulose (e.g. 35% w/w in DP600) and anisotropic solutions, first reported on non-derivatized cellulose. See Chanzy, H. and Peguy, A., J Polym Sci: Polym Phys Ed (1980) 18:1137-1144. However, the NMMO/H2O system has significant disadvantages associated with its use, e.g. high temperature required for dissolution; the degradation of cellulose; side-reactions of the solvent itself without an antioxidant (Potthast, A., et al., Holzforschung (2000) 54:101-103); and its high cost. The high temperature requirement is of particular concern since complete dissolution occurs only above 130xc2x0 C., which is close to the explosive point of about 150xc2x0 C.
Some thiocyanate salt aqueous solutions (Dubose, A., Bull Soc Ind Rouen (1905) 33:318-321; Williams, H. E., Mem Proc Manchester Lit Phil Soc (1921) 65:1-14; Williams, H. E., J Soc Chem Ind (1921) 40:221T-224T) and liquid NH3 solutions (Cuculo, J. A., et al., in Polymeric Materials Encyclopedia, Salamone, J. C., Ed., CRC Press: New York (1996) Vol. 2, pp 1029-1035; Scherer, P. C., J Am Chem Soc (1953) 53:4009-4013) are capable of dissolving cellulose. However, all of the combinations in the aqueous system need elevated temperature above 100xc2x0 C. for the dissolution, resulting ultimately in thermal degradation of the cellulose. It seems that water is not a powerful enough swelling agent for cellulose under mild conditions. The NH3/NH4SCN system has been disclosed for use as a solvent for cellulose (see e.g. Hudson, S. M., PhD Dissertation, Fiber and Polymer Science School of Textiles, North Carolina State University, Raleigh, N.C., United States of America (1981)); but, the system requires a condensation step to supply the solvent with liquid NH3 and in its use and/or storage, care must be exercised to minimize its volatilization to avoid subsequent crystallization of NH4SCN.
Blackwell et al. (Lee, D. M. and Blackwell, J., J Polym Sci: Polym Phys Ed (1981) 19:459-465) elucidated the structure of cellulose-hydrazine complex by X-ray diffraction. Hydrazine molecules interact with and break intermolecular hydrogen bondings network of cellulose chains. Under severe conditions, above 150xc2x0 C. and 5 atm, it dissolves cellulose (U.S. Pat. No. 4,028,132 to Litt, M. H. and Kumar, N. G. (1977)). However, this system is limited to closed systems and is extremely violent. See also Trogus, C. and Hess, K., Z Phys Chem (1931) B14:387-395.
Accordingly, there exists a need for compositions and methods that can be used, among other applications, in producing cellulosic articles (e.g. films or fibers) in an economically and environmentally acceptable manner. The present invention addresses these and other needs in the art.
Cellulose solvents, cellulose compositions, cellulose articles and methods of making and using the same are disclosed. For example, a cellulose composition comprises cellulose dissolved in the following solvent: an amine-based composition, provided however, the amine-based composition is not ammonia; and a salt selected from the group including a thiocyanate salt, a halide salt, and a nitrate salt.
Optionally, the amine-based composition has the general formula: 
where R1, R2 and R3 are the same or different, and R1, R2, R3 are selected from the group consisting of hydrogen, amino, alkyl, alkylamino, alkenyl, alkenylamino, alkynyl, alkynlamino, combinations thereof, and hydrated forms thereof; provided however, R1, R2, and R3 are not all hydrogen at the same time. Optionally, the amine-based composition is selected from the group consisting of hydrazine, hydrazine hydrate, and ethylenediamine.
The amine-based composition can be present in an amount ranging from about 20 to about 60 wt % and the salt can be present in an amount ranging from about 40 to about 80 wt %. Optionally, up to about 20 w/w % of cellulose is dissolved in the solvent, alternatively about 1 to about 15 w/w % cellulose is dissolved in the solvent. The cellulose composition can comprise an anisotropic phase.
Accordingly, it is an object of the present invention to provide a solvent composition for cellulose, a cellulose composition, and methods for making and using the same. The object is achieved in whole or in part by the present invention.
An object of the invention having been stated herein above, other objects will become evident as the description proceeds when taken in connection with the accompanying Examples and Drawings as best described herein below.